Automatically resettable thermal actuated switch



1. M. MILLER 3,264,437

Aug. 2, 1966 FIG. 1

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Inna flll-liffili 2 3 22 2. J22 l-I i I flm gm lLUlIII l IIIIHI I 3o 5-l-"llV/l v 30) L40 l7 23 a ('8 I X 12' 25' l5 f I' Il 9. f I l4 2| I 2440' INVENTOR. IMRICH M. MILLER United States Patent 3,264,437AUTUMATICALLY RESETTABLE THERMAL ACTUATED SWITCH Imrich M. Miller, 72 E.35th St, Paterson, NJ. Filed Sept. 6, 1963, Ser. No. 307,092 7 Uaims.(Cl. 200-414) This invention relates to a thermally actuated switch andmore particularly to a thermal actuated switch which is automaticallyresettable.

One form of switch which is currently in use is the so calledtemperature sensitive or thermally actuated switch which operates toopen or close a pair of contacts or other similar devices, upon sensinga predetermined critical environmental temperature. A common use forsuch a switch is an electrical circuit breaker in which the sensing ofthe elevated temperatures produced by an overload of current in theelectrical circuit causes the switch to open, thereby opening theelectrical circuit.

As is known, temperature sensitive switches generally use either abimetallic heat sensitive member or a meltable metallic alloy as thetemperature sensitive element to control the actuation of the switch. Inmany applications where a bimetallic member is used, such member usuallybeing two pieces of dissimilar metal which are joined together, thetemperature at which the switch is actuated by the bimetallic membercannot be controlled precisely enough. This is due to variations in thetwo metals forming the bimetallic member, variations in the lengths ofthe two pieces of metal, junction variations, etc. Therefore, inapplications where the switch must be actuated at a precise temperature,a bimetallic member might not be accurate enough to operate the switchat the correct time. This creates a potential hazard because damagesmight occur to the circuit in which the switch is located if thecritical temperature is exceeded before the switch opens. Where ameltable alloy is used as the temperature sensitive element, the meltingpoint of the alloy is more precisely controllable so that thetemperature at which the switch is actuated can be controlled moreaccurately. However, the use of such an alloy presents difiiculties inthe construction of the switch, and particularly where the switch is tobe automatically resettable.

The present invention relates to a thermal switch which uses both abimetallic member and an alloy as temperature sensitive elements toactuate the switch. The alloy is used as the principal temperaturesensitive element to control the actuation of the switch at a desiredcritical temperature. In accordance with the invention, the bimetallicelement and other elements arranged in a predetermined manner controlthe opening or closing of the switch in a manner so that the switchautomatically resets to its initial position when the environmentaltemperature has dropped below the critical temperature.

It is therefore an object of this invention to provide an automaticallyresettable thermally actuated switch.

A further object of this invention is to provide a temperature sensitiveswitch which utilizes both a bimetallic member and an alloy to controlthe actuation of the switch at a predetermined temperature.

Yet a further object of the invention is to provide an automaticallyresettable thermal sensitive switch which uses an alloy as thetemperature sensitive element.

Another object of the invention is to provide an automaticallyresettable thermal switch which is opened and closed upon each rise andfall of the environmental temperature above and below a criticaltemperature.

Other objects and advantages of the present invention will become moreapparent upon reference to the following specification and annexeddrawings in which:

FIGURE 1 is a side elevational view of one embodiment of the switch madeaccording to the present invention;

FIGURE 2 is a view, taken partially in section, of one type of alloyjunction for use with the switch;

FIGURE 3 is a plan view of the switch as used for driving a gear train;

FIGURE 4 is an elevational view of another embodi ment of the invention;and

FIGURE 5 shows another embodiment of the invention using a double-poleswitch.

Referring first to FIGURES 1 and 2, the automatically resettable switchof the present invention is formed by respective upper and lower contactarms and 12 having the electrical contacts 11 and 13 affixed thereto.The upper contact arm 10 is illustratively shown as being held in arelatively fixed position by a block 16 of insulating material which isconnected to a switch housing, switch-frame, or other type base member17. A pair of leads 14, are electrically connected to the respectivecontact arms 10, 12 at any desired position thereof. These leads connectthe switch into an electrical circuit (not shown) which forms no part ofthe present invention.

The lower arm 12 has a shaft 18 at its end remote from contact 13. Shaft18 is held within an alloy junction 20 which is held on a ratchet Wheel22. The ratchet wheel is pivotally mounted to the frame at 36. A pawl21, which is pivotally mounted at 23, holds the ratchet wheel 22 in afixed position and prevents clockwise rotation of the wheel. One end ofa thermal sensitive member 24 is connected to the lower contact arm 12by a pusher piece 25 of electrically insulating material. This pusherpiece is preferably mounted for limited pivotal movement, as shown, topermit free motion of the arm 12. The other end of member 24 is fixedlymounted to the switch frame or housing by an electrically insulatingmember 26. The thermal sensitive member 24 is preferably a piece of asuitable type of bimetallic material whose shape changes from one formto another upon sensing a predetermined temperature. Many suitablebimetallic materials of this type are well known in the art and nofurther description is needed therefor. A spring type catch 27electrically insulated from the frame by member 28 is also provided tohold the arm 12 in the position shown in FIGURE 1.

The alloy junction 20 includes a cup-shaped member 32 which is fastenedto the ratchet 22 and holds an amount of an alloy 34 therein. The alloy34 is a composition which will melt and become liquified at a certainpredetermined critical temperature. Many suitable alloys are known whichcan perform this function, for example, compositions of variousproportions of tin, lead, copper, etc. While the term alloy connotesthat at least two materials are combined, it is intended that a singlematerial for example lead, can be used at the junction if desired. Thealloy material 34 in the joint solidifies below the critical temperatureand fixedlyholds the shaft to prevent rotation of the wheel relativethereto. When the critical temperature is exceeded, the alloy melts andthe switch operates in a manner to be described.

As shown in FIGURE 2, the cup 32 has a cover 35 so that the switch maybe utilized with the ratchet wheel 22 in a vertical position. The coverprevents the alloy from running out of the cup when it is in a liquidstate. In this arrangement the shaft 18 is provided with a hub 19 whichextends through an opening in the cover to provide more surface area foralloy 34 to become effective in engaging and holding the shaft 18.

It should be understood that there are many possible mounting variationsfor attaching the alloy holder cup 32 to the wheel and for immersing theshaft 18 in the alloy. For example, the cup 32 may be mounted in anopening in the wheel 22 and either the wheel or the cup pivotallymounted to the frame. Also, the hub 19 on the shaft may be omitted sothat a smaller surface area contact is made between the shaft and thealloy. This may be desirable in some light contact quick opening switchapplications. It should also be clear that the cover 35 may be omittedfrom the cup if the switch is to be used in a horizontal position.

The critical temperature at which the switch is to be actuated isselected and the composition of the alloy 34 is chosen to melt at thisparticular temperature. The bimetallic member 24 is constructed to beflexed in the direction shown in FIGURE 1 when the environmentaltemperature is in a safe operating range somewhat below the selectedcritical temperature so that it urges the arm 12 toward arm 10. Thematerials for the member 24 are chosen so that the member flexes in theopposite direction to tend to pull the arms 11 and 12 apart when theenvironmental temperature is in a range of predetermined number ofdegrees below the critical temperature at which the alloy melts. Thetemperature at which member 24 flexes in the direction opposite fromthat shown in FIGURE 1 is preferably selected to be several degrees, forexample 10 F., below the melting temperature of the alloy. Of course,any suitable temperature differential between the flexure temperature ofmember 24 and the melting point of the alloy 34 may be selected.

Considering the operation of the switch, when the device with which theswitch is used is running normally, the environmental temperature willbe below both the fiexure temperature of member 24 and the criticaltemperature of the alloy. Under these conditions the bimetallic member24 pushes the two contacts 11 and 13 into engagement. During this time,the alloy 34 in the joint 20 is solidified and it firmly holds the shaft18 to prevent it from rotating in the joint. Since the bimetallicelement 24 limits the upward travel of arm 12 to the position shown, theratchet wheel 22 is prevented from rotating over the pawl in thecounterclockwise direction. At the same time, the pawl 21 prevents theratchet 22 from turning in a clockwise direction.

When the temperature rises to the point where the bimetallic member 24is to flex in a direction to pull the two arms 10, 12 away from eachother, this temperature being below the melting (critical) temperatureof the alloy, movement or flexation of the member 24 is still preventedat this time. This is so because the shaft 18 cannot move in thesolidified alloy in joint 20 and the pawl 21 prevents the ratchet wheelfrom moving clockwise. When the temperature increases further to thecritical temperature, the alloy 34 in the joint 20 melts and the shaft18 is free to move relative to the joint. After the alloy melts, thebimetallic member 24 flexes in the direction opposite to that shown andthe contact arm 12 is pulled away from arm with the shaft 18 rotating inthe joint 20. The movement of arm 12 breaks the electrical contactbetween elements 11 and 13. It should be understood that when arm 12moves downwardly there is still no movement of the ratchet wheel 22,since this is prevented by the pawl 21.

As described above, the switch contacts are automatically opened whenthe operating temperature exceeds the critical temperature. Theautomatic closing of the switch contacts when the operating conditionsare safe again, for example when a circuit overload has been removed, isdescribed below.

As the temperature decreases and goes below the critical temperature,the first thing that happens is that the alloy in the joint 20 freezes.This holds the shaft 18 of arm 12 fixed against rotation in the jointwhile contact 13 is still spaced out of engagement with contact 11. Atthis time, the temperature has not dropped sufliciently to permitbimetallic element 24 to flex back to its original position and push thearm 12 toward arm 10. However, as the temperature decreases further, thebimetallic arm flexes back to its original position and the arm 12 ispushed in the direction to engage contacts 11-13. Since rotation of theshaft 18 in the joint cannot occur at this time, the movement of arm 12turns the ratchet wheel 22 in the counterclockwise direction and thewheel is advanced one notch before the pawl is engaged again. Thus, theswitch is automatically reset with an advance of one step of the ratchetwheel.

As can be seen, the switch of FIGURES 1 and 2 opens its contacts uponthe alloy sensing the predetermined critical temperature andautomatically resets and closes its contacts when the temperature dropsa predetermined number of degrees below the critical temperature. Sincethe melting point of the alloy can be precisely selected, actuation ofthe switch at the critical temperature is assured with considerably moreaccuracy than could normally be obtained by using only a bimetallicmember. Also, the automatic resetting of the switch is advantageoussince it eliminates the need for an operator to perform this taskmanually.

FIGURE 4 shows a switch for closing a circuit upon sensing the criticaltemperature, rather than opening the circuit as shown in FIGURE 1. InFIGURE 4, the arm 10' is spaced below the arm 12'. Therefore, attemperatures below the critical temperature the bimetallic element 24flexes upwardly and holds arm 12 and contact 13' away from arm 10' andcontact 11. As the temperature increases to the flexation point ofmember 24, the member 24 tries to flex downwardly but is prevented fromdoing so since the contact arm 12 is frozen in the joint 20 and theratchet wheel 22 is held against clockwise rotation by the pawl 21. Asthe temperature increases still further, the alloy in the joint meltsand the shaft 18 is free to rotate. Therefore, bimetallic member 24flexes downwardly and pulls arm 12 down so that the contact members 11and 13 engage and close the circuit.

When the temperature starts to decrease, the switch of FIGURE 4 isautomatically reset to the open circuit condition in the followingmanner. First, the alloy in the joint 20 freezes the shaft 18 of arm12'. As the temperature goes still lower, the bimetallic member 24flexes back to its original condition and pushes arm 12 away from arm10' to break contact between elements 11 and 13. As arm 12 moves, theratchet wheel 22 is advanced one notch in the counter-clockwisedirection.

Either of the switches of FIGURES l or 4 can be converted into a doublethrow switch by providing another stationary switch arm 50 and contact51 in the manner shown in FIGURE 5. For example, using the switch ofFIGURE 1, the movable contact arm 12 is provided with contact members 13on both sides thereof. When the temperature is below the criticaltemperature, there is a circuit connection between the contact 13 on arm12 and the contact 11 on stationary arm 10. Now, however, when thecritical temperature is exceeded and arm 12 is pulled downwardly,contact 13 makes electrical connection with the contact 51 and completesanother circuit. This circuit, for example, could be an alarm circuit togive an indication that the critical temperature has been exceeded andthe main circuit through contacts 11 and 13 opened. Therefore, theswitch of FIGURE 5 can be used to control two electrical circuits withthe addition of arm 50.

A similar arrangement to control two circuits can be provided for theswitch of FIGURE 4 by placing the arm 50 above the arm 12. Here thesecond circuit formed by the contact 51 would be closed at temperaturesbelow the critical temperature.

It should be recognized that the thermal sensitive switch of the presentinvention has many uses. For example, it can be utilized as a circuitbreaker to open a circuit and as a thermal sensitive switch to close acircuit in any electrical circuit applications. The switch also can beused in mechanical or electro-mechanical applications.

For example, an electrically operated counter can be energized by apulse of energy each time the switch is opened or closed. If it isdesired to provide a thermal sensitive mechanical counter to sense thenumber of times the critical temperature is exceeded, a gear 40 or othersuitable drive member may be affixed to the ratchet wheel 22 of eitherof the switches of FIGURES l or 4. This is shown in FIGURE 3. The gear40 drives a suitable mechanical counter and the counter is advanced onecount for each rise and fall of the temperature through the criticaltemperature. Such a device may be useful, for example, where it isdesired to count the number of times that a particular device such as anoil burner goes on in any given period. Also, a counter or othersuitable device may be driven by the gear 49 and the electricalswitching operation still be provided in the manner previouslydescribed. As still another use for the switch, a contact arm (notshown) may be carried by wheel 22 or affixed to :the drive member 40 andthe advancement of the wheel one notch for each rise and fall of thetemperature through the critical point used to operate the contact armas the movable element of a stepping switch. Here, the stepping switchwould be temperature sensitive.

Therefore it can be seen that a novel thermal sensitive switch has beenprovided which is automatically resettable. The switch of the presentinvention is actuated precisely at a given temperature since it isprimarily dependent for its temperature sensing function upon an alloywhose melting point can be relatively precisely controlled. Also, sincethe switch is automatically resettable, it can be used in manyapplications where it is desired not to employ the services of anoperator. While the switch has been illustratively shown as moving onlya single contact or contact arm it should be understood that a pluralityof such arms can be moved at one time and/or each arm may carry aplurality of contacts.

While I have described preferred embodiments of my invention it will beunderstood that many other modifications may be made without deviatingfrom the principles thereof; therefore I wish to be limited not by theforegoing description, but solely by the claims granted to me.

What is claimed is:

1. An automatically resettable thermostat type switch which is operativein response to ambient temperature to change from a first to a secondoperative position comprising:

a movable contact arm,

a first thermal sensitive means connected to said contact arm forpositioning said contact arm at said first operative position inresponse to sensing temperatures below a critical temperature and tosaid second operative position in response to sensing temperatures abovesaid critical temperature,

a second thermal sensitive means connected to said contact arm forrestraining the positioning of the contact arm from said first to saidsecond operative position by said first thermal sensitive means until afirst temperature above said predetermined critical temperature issensed by said second thermal sensitive means and for preventing saidfirst thermal sensitive means from moving said contact arm from saidsecond to said first operative position until said first thermal meanssenses a temperature equal to or less than said critical temperature,and means for holding said second thermal sensitive means at apredetermined position during the time the temperature rises from saidcritical temperature to said first temperature and falls from said firsttemperature to said critical temperature.

2. An automatically resettable thermostat type switch as set forth inclaim 1 wherein said second thermal sensitive means comprises an alloywhich melts at said first temperature above said predetermined criticaltemperature and which solidifies at a temperature between said firsttemperature and said critical temperature.

3. A thermostat type switch responsive to ambient temperat-ure changescomprising:

a movable contact arm,

a first bi-directional movable thermal sensitive means connected to saidcontact arm for positioning it between first and second operativepositions in response to ambient temperatures respectively above andbelow a critical temperature,

a joint including a material which melts at a first temperature abovesaid critical temperature and solidifies in response to ambienttemperatures below said first temperature,

first means connected to said arm and having a portion :thereof incontact with the meltable material of said joint to permit the movementof said armby said first thermal sensitive means to said first positionwhen the ambient temperature reaches said first temperature and to saidsecond position only after the material has solidified and said criticaltemperature has been reached, and means in contact with said first meansfor holding said contact arm at said second position until said firsttemperature is reached and said material melts.

4. A thermostat type switch as set forth in claim 3 wherein said holdingmeans is a ratchet and pawl.

5. A thermostat type switch as set forth in claim 4 wherein said jointis mounted in said ratchet wheel and said wheel is moved by the contactarm going from said second to said first position when said meltablematerial is solidified.

6. A thermostat switch as set forth in claim 3 wherein said meltablematerial is located in a holder forming part of said joint, and saidholder is connected to said holding means.

7. A thermostat switch as set forth in claim 6 wherein said holdingmeans is a ratchet and pawl which moves one step for each cycling of thetemperature from said critical temperature to said first temperature andback to said critical temperature again.

References Cited by the Examiner UNITED STATES PATENTS Re 17,650 4/1930Kendig 200 124 1,659,862 2/1928 Dodge 200 124 1,678,878 7/1928 Sandin200 124 1,844,492 2/1932 Wilms 200 124 FOREIGN PATENTS 422,902 4/1933Great Britain.

BERNARD A. GILHEANY, Primary Examiner.

1. AN AUTOMATICALLY RESETTABLE THERMOSTAT TYPE SWITCH WHICH IS OPERATIVEIN RESPONSE TO AMBIENT TEMPERATURE TO CHANGE FROM A FIRST TO A SECONDOPERATIVE POSITION COMPRISING: A MOVABLE CONTACT ARM, A FIRST THERMALSENSITIVE MEANS CONNECTED TO SAID CONTACT ARM FOR POSITIONING SAIDCONTACT ARM AT SAID FIRST OPERATIVE POSITION IN RESPONSE TO SENSINGTEMPERATURES BELOW A CRITICAL TEMPERATURE AND TO SAID SECOND OPERATIVEPOSITION IN RESPONSE TO SENSING TEMPERATURES ABOVE SAID CRITICALTEMPERATURE, A SECOND THERMAL SENSITIVE MEANS CONNECTED TO SAID CONTACTARM FOR RESTRAINING THE POSITIONING OF THE CONTACT ARM FROM SAID FIRSTTO SAID SECOND OPERATIVE POSITION BY SAID FIRST THERMAL SENSITIVE MEANSUNTIL A FIRST TEMPERATURE ABOVE SAID PREDETERMINED CRITICAL TEMPERATUREIS SENSED BY SAID SECOND THERMAL SENSITIVE MEANS AND FOR PREVENTING SAIDFIRST THERMAL SENSITIVE MEANS FROM MOVING SAID CONTACT ARM FROM SAIDSECOND TO SAID FIRST OPERATIVE POSITION UNTIL SAID FIRST THERMAL MEANSSENSES A TEMPERATURE EQUAL TO OR LESS THAN SAID CRITICAL TEMPERATURE,AND MEANS FOR HOLDING SAID SECOND THERMAL SENSITIVE MEANS AT APREDETERMINED POSITION DURING THE TIME THE TEMPERATURE RISES FROM SAIDCRITICAL TEMPERATURE TO SAID FIRST TEMPERATURE AND FALLS FROM SAID FIRSTTEMPERATURE TO SAID CRITICAL TEMPERATURE.